(a) Field of the Invention
This invention relates to a device for generating a variable control signal, and more particularly to a device for generating a variable control signal of the type in which the control signal is generated in response to the manipulation of the device by an operator and is applied to suitable circuits as a control signal thereof, e.g., when the device is employed for audio equipments, such as voltage controlled amplifiers or voltage controlled filters, for controlling such as sound volume or sound quality.
(b) Description of the Prior Art
Recently, a new push-button type adjusting circuit for controlling such as sound volume, sound quality or the like has been used extensively in the fields of audio equipment in place of an old adjusting circuit which uses a variable type resistor. The known push-button type adjusting circuit comprises a device for generating a variable control signal in response to the depression or manipulation of a switch or a push-button, for controlling such as a voltage controlled amplifier or a voltage controlled filter.
One of typical examples of such push-button type adjusting circuits is illustrated in FIG. 1, for example, which is used in a sound volume adjusting circuit as one example.
The sound volume adjusting circuit particularly shown in FIG. 1 comprises a voltage controlled amplifier 1 for amplifying an audio signal the gain of which is varied in accordance with a control voltage Vc, and a control signal adjuster 2 which generates the control voltage Vc in response to the manipulation thereof by an operator. The control signal adjuster 2 comprises two push-button switches 3 and 4, a clock generator 5, two AND gates 6 and 7, an up-down counter 8, and a digital to analog (D/A) converter 9. Each of the push-button switches 3 and 4 is supplied at one terminal with a logical value "1", and the former is used for increasing a sound volume and the latter is used for lowering the sound volume. The clock generator 5 generates clock signals having a constant time interval therebetween. The other terminals of the two push-button switches 3 and 4 are coupled respectively to one input of the AND gates 6 and 7, the other inputs thereof being coupled to the output of the clock generator 5. Thus, the up-down counter 8 increases the count contents thereof upon reception of the clock signals from the AND gate 6 during the time the push-button switch 3 is being turned on, while the up-down counter 8 decreases the count contents thereof upon reception of the clock signals from the AND gate 7 during the time the push-button switch 4 is being turned on. The D/A converter 9 converts the counted value of the up-down counter 8 to the corresponding analog voltage (which is used as the control voltage Vc).
With the sound volume adjusting circuit constructed as above, the control voltage Vc of the control signal adjuster 2 is raised during the depression of the push-button 3 thereby to raise the gain of the amplifier 1 for higher sound volume, while the control voltage Vc is lowered during the depression of the push-button switch 4 thereby to lower the gain of the amplifier 1 for lower sound volume. With the application of the control signal adjuster 2, a sound quality adjusting circuit can be implemented by replacing the voltage controlled amplifier 1 in FIG. 1 with a voltage controlled filter, whereby sound quality can be varied similary as above described by depressing either one of the push-button switches 3 and 4.
In this control signal adjuster 2 shown in FIG. 1, difficulty has been encountered in some points particularly when the control signal adjuster is incorporated with the push-button type adjusting circuit for controlling sound volume or quality in audio equipment. Since the variation speed of the control signal Vc generated by the control signal adjuster 2 is determined in accordance with the time interval of the clock signals generated by the clock generator 5, there are tradeoffs to consider between the time interval of the clock signals and the operational facilitation of the control signal adjuster 2. More in detail with a shorter time interval of the clock signal, the variation speed of the sound volume or quality is increased, however, it is difficult to carry out a fine adjustment of the sound volume or quality. Conversely, with a longer time interval of the clock signal, the variation speed of the sound volume or quality is decreased, however, in this case, it is also difficult to carry out a quick adjustment of the sound volume or quality. Furthermore, since the adjustment of the sound volume or quality is performed by actuating the two push-button switches 3 and 4, it is naturally impossible to visually recognize the degree of the sound volume or quality at the time of manipulation.